The present invention relates to a radial needle-like roller bearing and a pinion shaft used in, for example, a planetary gear mechanism of a vehicular automatic transmission.
A planetary gear mechanism is generally used in an automatic transmission mounted to a vehicle or the like. Meanwhile, in recent years, also an automatic transmission tends to be formed by multistages with an object of improving fuel cost. At the same time, a planetary gear mechanism referred to as so-to-speak Ravigneau type is tried to be used to form an automatic transmission of 4 speeds as a main stream currently by mutlistages of, for example, 5 speeds or 6 speeds to downsize the automatic transmission. The Ravigneau type planetary gear mechanism is combined with two planetary gear mechanisms commonly using a planetary gear and is described in, for example Patent Reference 1.
Here, a characteristic of the Ravigneau type planetary gear type mechanism resides in that since a width in a axial line direction of the planetary gear commonly used is enlarged, a length in an axial line direction of a pinion shaft supporting the planetary gear relative to a diameter thereof is prolonged, that is, the pinion shaft becomes slender. Meanwhile, as shown by Patent Reference 2, as a rolling bearing for supporting a planetary gear in a general planetary gear mechanism, there is frequently used a radial needle-like roller bearing in which a needle-like roller is arranged as a rolling member between a pinion shaft serving also as an inner ring of the bearing and the planetary gear serving also as an outer ring of the bearing. However, although an such a needle-like roller bearing, there is generally used an all roller type which is not provided with a retainer in a background art, recently, there is a case of using a so-to-speak cage & roller type having a retainer for rotating the planetary gear at high speed. When a plurality or more of rows of rollers (rollers) are constituted by the all roller type, it is general to provide a guide ring for guiding end portions of the rollers (rollers) between the rows. In contrast thereto, according to the cage & roller type, even when a plurality or more of those of rollers (rollers) are constituted, it is general that the guide ring is not provided since the retainer guides the end faces of the rollers (rollers).
[Patent Reference 1]
Japanese Utility Model Application Publication No. Hei4-126055
[Patent Reference 2]
Japanese Utility Model Application Publication No. Hei5-62729
Here, in a planetary gear mechanism, a planetary gear is revolved to move and therefore, a centrifugal force operated to the planetary gear and a force of being brought in mesh with other gear elastically deform a pinion shaft. Although hardened steel is normally used for the pinion shaft, owing to a retained austenite structure inevitably present therein, in using the pinion shaft at a high temperature equal to or higher than 100° C., the retained austenite structure is disintegrated to expand a volume thereof. When the pinion shaft is elastically deformed at 100° C. or higher, a rate of disintegrating the retained austenite structure at a portion of operating a tensile stress faster than at a portion of operating a compressive stress and therefore, generally, the remoter from the portion of the pinion shaft attached to a carrier, the more the plastically bending is brought about in a bow-like shape, and the higher the temperature of the shaft, the faster the speed of revolving the planetary gear, further, the slenderer and the longer the pinion shaft, the higher the torque loaded to the gear, the more the rate tends to increase.
Particularly, when the Ravigneau type planetary gear mechanism disclosed in, for example, Patent Reference 1 is used for downsizing the planetary gear mechanism of a vehicular transmission of an automatic transmission or the like, there poses a problem that plastic bending of the long pinion is liable to be brought about since the shaft length is prolonged. When a sum of the plastic bending and elastic bending determined by loading conditions of the shaft which increases agingly is increased and a distance between the shaft and an inner diameter face of the pinion gear becomes smaller than a roller diameter, there poses a problem that the roller (roller) cannot smoothly be rolled and flaking is brought about at the shaft or the roller (roller).